#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#define WINDSIZEX 100
#define WINDSIZEY 100


static void Draw()
{
   GLubyte bitmap[] = {0xff, 0xff, 0xff};

   glDepthFunc(GL_ALWAYS);
   glColor4f(0.0, 0.0, 0.0, 1.0);
   glRasterPos3f(0.2, 0.2, 0.6);
   glBitmap(3, 1, 0, 0, 0, 0, bitmap);

   glDepthFunc(GL_LESS);
   glColor4f(1.0, 0.0, 0.0, 1.0);
   glRasterPos3f(0.2, 0.2, 0.0);
   glBitmap(1, 1, 0, 0, 0, 0, bitmap);
   glRasterPos3f(1.2, 0.2, 0.5);
   glBitmap(1, 1, 0, 0, 0, 0, bitmap);
   glRasterPos3f(2.2, 0.2, 1.0);
   glBitmap(1, 1, 0, 0, 0, 0, bitmap);
}

void init(void)
{
   glDisable(GL_DITHER);
   glEnable(GL_DEPTH_TEST);
}

static void test(void)
{    
   GLfloat buf[9];

   glClear(GL_COLOR_BUFFER_BIT);

   Draw();

   glReadPixels(0, 0, 3, 1, GL_RGB, GL_FLOAT, buf);
   printf("draw pixel at (0, 0): %f %f %f\n", buf[0], buf[1], buf[2]);
   printf("draw pixel at (1, 0): %f %f %f\n", buf[3], buf[4], buf[5]);
   printf("draw pixel at (2, 0): %f %f %f\n", buf[6], buf[7], buf[8]);
}

void display(void)
{
   glViewport(0, 0, WINDSIZEX, WINDSIZEY);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(0, WINDSIZEX, 0, WINDSIZEY, 2.0, -2.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();

   test();
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
   glutInitWindowSize(WINDSIZEX, WINDSIZEY);
   glutInitWindowPosition(100, 100);
   glutCreateWindow(argv[0]);
   init();
   glutDisplayFunc(display);
   glutMainLoop();
   return 0; 
}